Solar Air Heater Comparison! - Steel Can Heater vs. Screen Absorber Heater (temp. tests) 

Airflow thru the unit is important, to much airflow will lower the temperature. It has to be the correct airflow.

@@stevenbusman correct, there is a happy middle ground in the efficiency balancing the heat input and the airflow.

hi and thanks! since they operate by trapping the heat, the collectors wouldn't work much at all without the glass or plexi-glas.

Did you build it?

I think the air moves through it faster

great info man!

The longer the air stays in the collector, the hotter it will become. Without a fan, the air in yours was nearly stagnant, allowing maximum temperatures rise. With a blower moving the air, it limits the amount of time the air is within the collector. You can regulate the fan speed, to increase or decrease the temperature. The key is to find a balance between temperature and volume, to produce a useful amount of heat.

More Mass however will also take longer to heat up. You can balance them to your use. Your fan will stop long before the heat is extracted -add a small Li-on battery to keep your fan going during light shade.

The point of a solar collector is to turn as many solar rays into heated air, and move that heated air to get that energy out of the solar collector before that heat energy is lost to radiative or convective heat loss. The down side to more thermal mass and lower surface area absorber is that it has to get hotter to give up heat to the air. Think about this, 1 square meter has to get hotter than 10 square meters to heat the same volume of air in the same time frame. Being the absorber is hotter results in radiating more energy away as infrared light vs heating air as can be seen with thermal imaging. One can still intigrate thermal energy storage with a box of rocks resting on a wire screen layed over a wire mess and blocks supporting the wire mess. Hot air from the collector can be fed up through the rock providing a lot more thermal mass and surface area to quickly store or give up heat energy. When the air inside the solar collectors is the same or below temperature inside the home, forced air is then be diverted from from the collectors and fed strait into the thermal storage. Being fed room temperature air, the rocks would then give up their stored heat energy.

Any interesting and valuable point. I was thinking of using this for greenhouse heating and pumping it into a thermal mass battery anyway so it still works for me. I suppose the same could be done for a home, but that's a little bit more difficult than just burying the duct in some dirt.

What Keith and Daniel said. Check out Kirchoff's law. More mass = more time to get up to temperature. More heat sitting in a collector that's shaded = more radiant heat loss. That would = far more than just 3-5% less efficient. Generate and move that heat as quickly as possible. An ideal collector will have high thermal conductivity, low mass, and low emissivity. All solar collectors designed and tested with thermal mass have proven to be less efficient, and not cost practical. It's a waste of material.

@@kreynolds1123 Fire bricks, used in Air tight wood burning stoves. Thanks for the idea.. I'm building my first collector as we speak.

Can you be more specific on that? Are you talking about Venetian blinds?

Do you have a youtube video of your system ?

Did you ever do it?

Extra work for what ? You now can build this with a variety of stuff you have around house without a big diff in temp

Richard Berube like a solar oven?

@@momof1576 not a mirror, maybe a mylar spaceblanket or parabolic dish.

Hinged, covers unit during cooling season?

what about thick aluminum foil glued to all the inside walls?

Thinking about this, all heat absorbed to rear wall also contributes to heat production so getting more sun to cans might not make much difference, just thinking.

Lower temperature is actually better if it's outside. The hotter you let it get, the faster it will lose heat back to the environment. So more of your energy is wasted when the temperature is higher.

@@craigheimericks4594 Mine was set up to sit on a window sill inside. Wasn't my home so I couldn't make holes in the walls.

clearly the popcan one

The solar panel in between the 2

I disagree. Leave both can ends on...The more mass you can leave/install, the more heat will be available to heat flowing air. A few holes in BOTH ends to allow for air flow might work fine. Better yet, fill the can assemblies with massive of some kind, maybe ball bearings? Lots of mass, lots of air flow passage between the bearings.

@@dantyler6907 i happen to have a small collection of ball bearings i was saving for such a project.

What would be the cost for somethings like black aluminum photo foil...going to have to research that term...LOL!

I got 12 inch by 10 foot roll for like 9 dollars. I think you can even find it cheaper.

Hello TRON where can I get black aluminum photo foil? Thank

Any (photographic) studio supply store. I work in a camera store, we have rolls of it. Cinefoil, is the brand.

Lets look at two hypothetical solar collectors of the same size and color. One is aluminum foil linning spray pained black. Light hitting it is absobed and is converted to heat. It gets much hotter than the air above it. For this discussion we can ignore the surfaces below. Some of that heat is given up to the air above it, but that is limited due to air flow and surface area. Also because it is hot, some energy is radiated as infrared light out to space. The hotter a surface is, the more efficent it both radiates infrared light. If the same amount of sunlight falls on a larger surface area like a screen or fiberglass insulation spray painted black, the substance does not get as hot as the light is collected over a larger surface area that is also incontact with more air inside the collector. And because of the energy is more quickly given over to heat the air, less energy is lost to infrared light making the high surface area solar collector more efficent.

what you gain in heat would be lost in efficiency :) Its best to run the output just slightly higher than what you need and move more air.

If you watch the instructional videos you will see that he uses multi layered cardboard that is glued in & painted black to insulate

Thermal energy storage inside the solar collector: Sand, rock, tiles, or metal, is a bad idea because during the day you are collecting solar energy, but during the evening and night, as you pass air through them to collect that energy, they are also radiating energy as infrared light out to space. The quicker you can get heat out of the solar collectors, the more efficent your solar collector will be. One can still intigrate thermal energy storage inside their home for better heat during the evening and into the night. But, when the sun goes down, air flow into the sollar collectors is shut off preventing them from being thermal radiators over night.

you make your point very well but I see where isheian is coming from. the fact is that many properties would have adequate heating in the morning hours already from an overnight electrical storage heater and strictly speaking probably don't need the extra from these solar collectors during the day. Isheian mentions sand and there are other materials used in storage heaters that you mention. it doesn't seem impossible to develop an apparatus that would blow out the retained heat from an adapted solar collector after darkness .After al if it works for electric over-night heaters why not for sola rcollectors?

hi and thanks. although they may look different lengths they are exact same ✔ (neither one was ever cut down)

I'd like more info on how you did that

hi. yep, the fans are the same.😎

Ideally, solar collector both minimizes their thermal mass and maximizes surface area to increase their efficency. In short, the point is quickly get the energy to heating the air, and to move that air out of the collector before the energy radiates away.

hi. feel free to check out the whole channel. i've got about 300 videos posted. some of the best never really got much 'traction' - lots of factors to all of it. most (if not all) of my videos are the "evergreen type' meaning that they are relevant even if they were posted a while ago. the editing isn't the best in some of my earlier videos but i did the best i could

Can't see why it wouldn't. I guess the steel cans are just a low cost easy to get alternative.

@@JosuRibeiro Yeah, that's a good point. I mainly ask because I've seen it be suggested that if you make the path for the air to move through longer, you end up getting less actual heat in your output. The same goes for if you restrict the air too much. I just wanted to verify that.

interesting... i'm not from mass but i did spend some time there.

@@desertsun02 I don't know, if where you live, there are businesses that resell DVDs and Blu-rays at CD. But if there are, or if you want to go out and buy a few on Amazon, there was a fantastic documentary called Apollo 11 that was produced back in 2019. I highly recommend it! Add you will hear Jack King voice over throughout most of the beginning of the presentation. And, you will notice that his voice is literally to pick with us to the voice of NASA!

You are likely comparing apples to orangess here. In order to properly compare performance you need to establish whether the air flow is the same. Having the same fans and size of box does not mean you have the same airflow because the internal airflow resistance is different. Calibrate each unit by shading the unit and then putting a known amount of heat like a 100 watt light bulb inside the inlet duct. Measure the outlet temperature of each unit and if they are the same temperature then they have the same air flow rate. If not then you are comparing apples to oranges and your conclusions are wrong. Airflow is proportional to delta T so you can use the results of your calibration test to see which one is performing better.

I say skip the outside build and make a box to fit inside your window inside the house. No need to buy plastic or glass doing this way. Worth a try.

Would you just use the solar panel for that? Seems redundant and inefficient to convert solar power to heat to power.

Just use fresnel lens directed on the piston of the stirling engine, lots of videos on here about that

The cans will still stay warm even in cloudy weather. There is still light to be collected and converted to heat, albeit not as much as if it was exposed to full sunlight.

Any idea why the 2x4 frame is hotter?

@@fetymann Less space to heat up that's all.

hi. since my videos are the "evergreen" or timeless type, you're never late 🙂👍

Should be the same for any collector, it is the suns heat, not out side temp. But better insulation on the outer sides & back may help some what.

Dwight Gordon will work but remember it the air being drawn through the collector is that the bottom so if you place this outside and do not pipe in the supply air to The Collector it will not heat up the air to the temperature you require I would recommend placing this inside the house in a window as an experiment before you go to the trouble of making holes through your home they do work I have built one or two of them to heat the garage helps offset the heating cost I to live in a very cold climate getting down to the -30 C here in Northern Canada

Jon Minnella - What's this all aboot?

I'm making my way through the youtubes for research now and the best option I've seen is to star with warmer air. Either put your box inside, or pipe house air outside into the panel and back in. Reckon you could put 2 in series if you were fixated on getting fresh, warm air.

A single glass panel has a u factor of around 1.22(R 0.8) which means 1.22 btu per sq/ft per hour per degree F of temp difference... if those are 2’ X 3’ collectors they have 6sq/ft of surface. With 45F air in and 120F air out at I am guessing around 45 CFM that panel is outputting about 3400 btu/hr. The panel mean temp would be around 82F. At 45F outside that is 37F difference. So 1.22 X 6X37 = 270btu per hour heatloss back thru the glass. The thin back would be similar but less as it isn’t as hot and the edges would loose at a lesser rate. Total losses would be probably less than 500 btu/hr though, or about 1/7 of the output. Insulating sides and back would help significantly

Yes, but then you won't get any heat while the cans are heating up :(Additionally, some stored heat will leak from the frame in the infrared spectrum.Best just to grab as much heat from the system as quickly as practical.

@@barleyeducated8714 exactly right on.

Would have to make sure each are 100% airtight between transfers, and also ensure that airflow is as efficient as possible. If done properly I believe it would increase efficiency

+Bill s . Remember, once the sun's rays penetrate the window, that heat is already in the room.

+Elaine Howard Biber Yes, that is certainly true, but with the collector working with already somewhat heated air, wouldn't it produce even hotter output with zero radiant leakage since it is entirely inside the structure already?

+Jim Smith Sr. I'm no thermodynamics expert, but I don't think so. Wouldn't the room just get hotter and hotter without limit ? Once the heat from the sun is inside the room that quantity of heat is fixed. If you use it to heat up the collector then that sun light is not heating up other surfaces that the collector obstructs.

hi there. on your first question, they can survive years (even decades) but it's going to depend on your climate, how well you seal it up and if (and how) you treat the wood etc... on the second question, those computer cooling fans are specifically designed to handle the same level of heat as in the collector so they should last their normal life span (which is typically 30,000 to 50,000 hours - in other words decades). those fans are typically 2 or 3 watts, so i generally recommend a 5 watt panel or higher. that way even when the sun is at an angle or it's slightly cloudy, it will keep running strong.

thanks a lot man... one last question: i have a cold room that due to the house -construction i must push the hot air from some 5 or 6 meters above. will this heater be able to send the hot air 5 or 6 meters Down to the room? thanks

The heat probably wouldn't last long enough to make a difference. Maybe get 5-10 mins of heat from it.

hi. it's good idea. i haven't been able to find vantablack on sale to the public yet. they sell it to some businesses i guess, but it's hard to get. i'll keep looking

@@desertsun02 i think black 2.0 would be better since its easier to get

i looked into black 2.0, but it when it dries it can look a little bit like dark grey (i've heard). they do have something called black 3.0. i think i might try that. it is not supposed to look grey once it's dried.

Rev John O'Toole hahahaha

andersenchrhome hi there. since the fans are identical (same make and model) and both running full speed (39.02 CFM) the flow is nearest to equal as i can make it. *power draw of each fan is 1.8w. (15w panel used)

desertsun02 Yes, BUT...the airflow needs to be fairly identical over the solar collection media. It would appear that the cans only have a few small holes in the top of each stack. I would conside opening them up much more. Either 1/2 in holes where those reside, or just one big 2 inch hole saw cut. Additionally, I don't know how long those panels sat in full sun before the test, but the much higher mass of the steel cans cold be providing a sink for the heat gained inside the box. This will result in a lower average temp, but a longer duration of heat when sun goes down/behind a cloud. This would be like measuring the heat of cast iron pan and a sheet of aluminum foil over the same flame. The foil will get hotter much faster, but will also cool faster when the heat source is removed... IDEA: how about using heavy blackened aluminum foil only as your collection grid, possibly using the cans as a "wave" mold? This would allow a large surface area for the air to pick up the thermal energy collected. Also, a bit more work, but you can collect more immediate heat if you make the fan collect the heat more evenly over the grid. This is easily done by putting more holes along the top of the box where the fan is now and making another box on top of those, with the fan pulling from that box. The holes at the outer edge should be larger and getting smaller to the center to allow the most even airflow. In the end, you'll get the same TOTAL heat, but this will just allow higher temps in the near term via better airflow over the collector. I build solar water distilleries and have learned to optimize the solar collection over time. I've had great success doubling my heat collection with simple panel concentrators, but you do have to track the sun more with those....Good Luck!

I wish you were my neighbor. I can build. I just don't visualize these awesome ideas like y'all.

hi. there's no noticeable or discernable difference in the airflow rate between the two. its about the same in both.